Mineral List

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality
is based on relatively small scale geological maps provided by various national Geological Surveys.
This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Description: The Golconda terrane is composed of deformed and imbricated thrust slices of upper Paleozoic rocks including deep-marine, pelagic and turbiditic, carbonate, terrigenous clastic and volcaniclastic rocks, radiolarian chert and argillite, and pillow basalt (Silberling, Jones, and others, 1992). While the terrane is characterized by a great diversity of rock types, all rocks are strongly deformed with an east-vergent fabric, a distinguishing characteristic of this terrane (Brueckner and Snyder, 1985; Jones, 1991a; Miller, Kanter, and others, 1982; Murchey, 1990; Stewart, Murchey, and others, 1986). It crops out in a long sinuous belt, up to 100 mi wide in places. Southwest of Mina, the belt trends east from the California border to just north of Tonopah, and then bends north-south to the west of Longitude 117° to about 50 mi north of Winnemucca, where it bends again, sharply to the east-north of Tuscarora with significant exposures eastward and to the northern border of the State. Outcrops of the Golconda terrane are present in Mineral, Esmeralda, northern Nye, Churchill, Elko, Humboldt, Lander, and Pershing Counties. It includes some rocks originally mapped as Banner and Nelson Formations in Elko County; rocks originally mapped as the Excelsior Formation in Mineral and Esmeralda Counties, later assigned to the Black Dyke and Mina Formations by Speed (1977b); the original Havallah and Pumpernickel Formations (Muller, Ferguson, and Roberts, 1951; Roberts, 1964; Silberling and Roberts, 1962), later revised to structural sequences (Murchey, 1990; Stewart, MacMillan, and others, 1977; Stewart, Murchey, and others, 1986; Theodore, 1991; 1994) in Elko, Humboldt, Lander, and Pershing Counties; the Inskip Formation in Pershing County; the Mitchell Creek Formation in Elko County; the Pablo Formation in northern Nye County; and the Schoonover Formation (see unit GChr) in Elko County. In all of the places where rocks of the Golconda terrane were originally believed to form a stratigraphic sequence, detailed mapping and biostratigraphic analysis with radiolarians and conodonts has demonstrated that it is characterized by complex imbrications of rocks ranging from mid-Permian through latest Devonian age (Holdsworth, 1986; Jones, 1991b; Miller, Holdsworth, and others, 1984; Murchey, 1990; Stewart, MacMillan, and others, 1977). In Pershing County, the Golconda terrane is unconformably overlain by Triassicvolcanic rocks of the Koipato Group (TRkv) which form the stratigraphic base to the Humboldt assemblage (TRc, JTRs). In Mineral and Esmeralda Counties, it is unconformably overlain by the Gold Range assemblage (JTRgor) of mainly nonmarine, terrigenous clastic, and volcanogenic Upper Triassic and younger rocks. Elsewhere in northern and southwestern Nevada, it is structurally overlain by Mesozoic accreted terranes. Across the length of its exposure from the Independence Mountains north of Elko to the Candelaria region south of Mina, the base of the Golconda terrane has a remarkably consistent structural emplacement relationship with adjacent rocks. It commonly lies on a low-angle structure above Permian and Pennsylvanian rocks of the Siliciclastic overlap assemblage. In places where these rocks are missing, it is faulted directly onto either the nearby lower Paleozoic Basin assemblage, the Nolan belt rocks, or the Harmony Formation of the Dutch Flat terrane. The type locality of this regional feature, the Golconda thrust is well exposed along Interstate Highway 80 at Edna Mountain near the town of Golconda (Ferguson, Roberts, and Muller, 1952), and in the open pits of mines near Battle Mountain (Theodore, T., oral commun., 2006). In southwestern Nevada, the lower Lower Triassic rocks of the Candelaria Formation overlie Permian and Pennsylvanian Siliciclastic overlap assemblage rocks, and the Golconda terrane is exposed nearby, but not observable directly on top of the Candelaria because of younger cover rocks. Elsewhere, there is no youngest age constraint for the age of emplacement. In several places, notably in the Osgood Mountains and the Toiyabe Range, it is also bounded by large, steeply dipping, mélange-like shear zones against older rocks of the Nolan belt. Stratigraphic and structural studies within the terrane have locally identified lithostratigraphic groupings (Erickson and Marsh, 1974a, b; Jones, 1991a; Murchey, 1990), but only the Home Ranch subterrane can presently be distinguished on a regional scale (GChr). Interpretations of the size and character of the late Paleozoic basin where these rocks formed and the nature of its Late Permian or Early Triassic accretion are as varied as the lithologic and structural characteristics of the terrane itself (see references above).

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